1. Field of the Invention
The present invention relates to a light source device for endoscope that applies illumination light that is combination of light from two or more light sources to an object of interest, an endoscope system, and a method for operating a light source device for endoscope.
2. Description Related to the Prior Art
Diagnoses using endoscope systems are widely performed in medical fields. The endoscope system comprises a light source device for an endoscope, an endoscope, and a processor device. The light source device generates illumination light applied to an object of interest (e.g. mucosa) in a body cavity. A light source (e.g. a xenon lamp) that emits light (hereinafter referred to as the continuous-spectrum light) having a broad continuous spectrum has been used as the light source device. Recently, however, a semiconductor light source (e.g. an LED (light emitting diode) or the like) has been replacing the broadband light source (e.g. the xenon lamp). In the case where the semiconductor light sources are used as the light sources, for example, two or more types of semiconductor light sources (e.g. a blue LED, a green LED, and a red LED) that emit light beams of different colors are used in combination. Thereby the light beams (hereinafter referred to as the multicolor spectrum light) having an optical spectrum (hereinafter may simply referred to as the spectrum) into which the spectrums of the light beams of different colors are combined are used as the illumination light.
For example, a light source device for an endoscope in an endoscope system described in US2015/0092035 (corresponding to Japanese Patent Laid-Open Publication No. 2013-255655) has four semiconductor light sources controlled independently. A spectrum, in which the light quantity distribution varies at each wavelength, of the illumination light is adjusted by controlling a light emission quantity (the light quantity) of each semiconductor light source. Thereby the object is irradiated with the illumination light having the properties suitable for the properties of an image to be captured. To be more specific, the spectrum of the illumination light is adjusted to capture, for example, an image with wide dynamic range of brightness, an image with low color temperature, an image with high color temperature, an image under the illumination of special narrowband light applied to a small area, or the like.
An endoscope system described in Japanese Patent Laid-Open Publication No. 2013-202166 has two or more semiconductor light sources controlled independently. The endoscope system identifies the model of the endoscope used and sets the conditions for driving each semiconductor light source in accordance with the model of the endoscope. To be more specific, the model of the endoscope is identified to set the light quantity ratio among the semiconductor light sources in accordance with the light transmission characteristics of a light guide, which transmits the illumination light, because the light transmission characteristics of the light guide varies according to the model.
As described above, with regard to the illumination light used in the endoscope system, the multicolor spectrum light of the semiconductor light sources is on its way to replace the continuous-spectrum light of the conventional xenon lamp or the like. The continuous-spectrum light is different from the multicolor spectrum light in spectrum. An image of an object captured under the illumination of the continuous-spectrum light may look different from an image of the object captured under the illumination of the multicolor spectrum light. Which one of the image captured under the illumination of the continuous-spectrum light and the image captured under the illumination of the multicolor spectrum light is suitable depends on circumstances. However, the adjustment of the multicolor spectrum light is easier than that of the continuous-spectrum light because the semiconductor light sources are controlled independently to make the spectrum of the illumination light suitable for the object.
For a long time, many doctors have been using the endoscope system utilizing the continuous-spectrum light of the xenon lamp or the like as the illumination light. Such doctors are accustomed to the images of an object captured under the illumination of the continuous-spectrum light. For this reason, it is necessary that the images captured under the illumination of the multicolor spectrum light of the semiconductor light sources can be observed in a comparable manner to those captured under the illumination of the continuous-spectrum light (in other words, it is necessary that the images captured under the illumination of the multicolor spectrum light are able to be compared with those captured under the illumination of the continuous-spectrum light). Many endoscopic images stored in past cases were captured under the illumination of the continuous-spectrum light. It is necessary to make the endoscopic image captured under the illumination of the multicolor spectrum light comparable to the endoscopic image captured under the illumination of the broadband continuous-spectrum light, to compare them easily.
To meet the above-described necessities, the spectrum of the broadband continuous-spectrum light may be reproduced using the semiconductor light sources. Actually, however, it is impossible for the semiconductor light sources to completely reproduce the spectrum of the broadband continuous-spectrum light. For example, in the case where the light sources are a blue LED and a green LED and a light quantity of each of the LEDs decreases as the difference between the center wavelength and the wavelength of the illumination light increases, it is difficult to change the light quantity of the light of the color between blue and green (the light in a wavelength range located at about the midpoint between the blue and green wavelengths) only by adjusting the light quantities of the blue and green LEDs. In the case where the light quantity of the light at the center wavelength emitted from each of the blue and green LEDs is made close to the light quantity of the broadband continuous-spectrum light, the light quantity of the light of the color between blue and green is substantially less than that of the broadband continuous-spectrum light. In the case where the light quantities of the blue LED and the green LED are increased to make the light quantity of the light of the color between green and blue close to that of the broadband continuous-spectrum light, each of the light quantity of the light at around the center wavelength of the blue LED and the light quantity of the light at around the center wavelength of the green LED significantly exceeds the light quantity of the broadband continuous-spectrum light.